Choosing the right mate is just as important for plants as it is for humans. As a rule, plants select a match within their own species to pass on all the correct genetic information to their offspring. But occasionally, a plant opts for an altogether different mate, and the genetic mix creates an entirely new species. Daphne Preuss is investigating the mechanisms that control how plants choose mates and the cellular machinery that evolves as species diverge, including the DNA and proteins that direct chromosome segregation and the genes that dictate reproduction. Ultimately, her studies may help scientists manipulate the flow of genes between species to create new, hardier crop varieties and to keep in check the mating of genetically modified plants.
Preuss developed a love for science as a child by reading biographies of famous scientists, including Thomas Edison and Marie Curie. Learning about their lives made Preuss realize that she, too, wanted to be a scientist, but she had no idea how to go about it. The small, rural Colorado community in which she lived offered no scientists, let alone women scientists, as role models. "The thing that would have meant the most to me was seeing a woman, even on television, who was a scientist," she said.
Not to be deterred, Preuss carved out her own path. After graduating with honors from the University of Denver, she landed a coveted spot in MIT's doctoral program in biology. Initially, Preuss studied yeast genetics but later chose to focus on plants, specifically Arabidopsis thaliana, the plant kingdom's version of the simple fruit fly. Scientists were just beginning to use genetic and molecular biology techniques to investigate plant cell biology, and Preuss thought these approaches would reveal a lot about plants' distinctive interactions, including the way they choose mates. "Plants have to interact with whatever pollen is scattered their way, but they have developed sophisticated ways to discriminate between pollen from their own species versus pollen from another species," she noted.
During a postdoctoral fellowship at Stanford, Preuss made a surprising discovery that has guided her research ever since. While peering through her microscope to look for mutations that affect the shape of pollen, she spotted four pollen cells stuck together on a slide. This anomaly, a tetrad, occurs when cells dont separate properly during meiosis, a special type of cell division used to produce eggs or sperm. Its presence in Arabidopsis has allowed Preuss and others to track the way chromosomes swap bits of DNA and then divide in the course of meiosis, a process that had been poorly understood in all plants.
Preuss's studies have identified genes that code for proteins that coat the pollen of Arabidopsis, a finding that is helping scientists understand how plants recognize pollen from their own species. Manipulating pollen recognition by altering pollen coat proteins may enable crop scientists to cross previously incompatible plant species, such as cold-resistant apple trees with other trees that bear tasty fruit, or prevent genetically engineered plants from crossing with other strains. She and her colleagues also have found that one of the brain's most important neurotransmitters, γ-amino butyric acid (GABA), is a key signaling molecule in plants that directs the formation of the pollen tube, an important first step in fertilization whereby plant sperm are directed toward the egg of the flower.
Preuss's pollen research recently has led her in a new direction: to identify the molecules within pollen that trigger allergies. Specifically, she is exploring proteins and lipids that coat pollen grains, molecules that previously have been overlooked as the source of allergies. This line of research may one day provide more effective treatments for the millions worldwide who experience watery eyes, runny noses, coughing, and sneezing when exposed to airborne pollen.
Daphne Preuss is Professor of Molecular Genetics and Cell Biology at the University of Chicago, where she is also a member of the Institute for Biophysical Dynamics.
RESEARCH ABSTRACT SUMMARY:
Daphne Preuss is investigating the cellular machinery that evolves rapidly as species diverge, including the DNA and proteins that mediate chromosome segregation, the genes that control reproduction, and the signals that trigger allergy.
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Photo: Mark Segal